1. Field of the Invention
The present invention relates to improvements of ball valves for medium and low pressure service.
2. Description of the Prior Art
FIG. 1 is a sectional view of a conventional ball valve, and FIG. 2 is a right side elevation thereof. A valve body 1 is made of a hexagonal tubular body, and internal threads 2a, 2b are cut for connection with joints. A cylindrical passage 3 is machined in the valve body 1, and a spherical valve member 4 held by a pair of sealing members 6a, 6b is placed in this passage. One sealing member 6a is prohibited from displacement in the axial direction by a threaded ring 5 screwed into an internal thread 7 which is continuous to the internal thread 2a. The other sealing member 6b is prohibited from displacement in the axial direction by abutting against a stepped part 8 formed in the valve body 1. The threaded ring 5 abuts against a stepped part 9 formed in the valve body 1.
In such prior art arrangement, if the length in the axial direction, that is, the thickness, of sealing members 6a, 6b is small, and when the outside diameter of valve member 4 is small, a gap is produced between the outer circumference of the valve member 4 and the sealing members 6a, 6b, which gap spoils the enclosing function of the valve construction. To the contrary, when the thickness of sealing members 6a, 6b is great, and when the outside diameter of the valve member 4 is large, it is impossible to tighten the threaded ring 5 until it abuts against the stepped part 9, and if it is attempted to force such tightening, the sealing members 6a, 6b and valve member 4 are brought into tight contact, thereby making it difficult to rotate the valve member 4. In this case, if the threaded ring 5 is tightened in a state permitting easy rotation of the valve member 4, the threaded ring 5 may be easily loosened by vibration or temperature changes. Therefore, the threaded ring 5 must be tightened firmly until it abuts against the stepped part 9. Hence, in order to achieve the desired degree of tightness by accommodating the sealing members 6a, 6b and valve member 4 into a fixed space determined by the valve body 1 and threaded ring 5, high dimensional precision of the sealing members 6a, 6b, and valve member 4 is required. As a result, productivity is lowered, and cost is increased.
This prior art arrangement is applicable for high pressure fluid. However, conventionally, such prior art arrangement has been applied for medium to low pressure fluids, such as town gas and water. When such prior art arrangement is used for medium to low pressure fluids, such use is a waste of materials.
An end of a drive shaft 10 is fitted to the valve member 4, and a handle 12 is fitted to the other end of the drive shaft 10 by way of nut 11. At the bottom of the handle 12, a stopper 13 is bent toward the side of valve body 1. When the stopper 13 abuts against the outer wall of the valve body 1, the valve member 4 may be set in the fully closed or open state. In such prior art arrangement, the valve member 4 may be displaced angularly and the valve opening degree may vary when the handle 12 receives an external force or when vibration occurs.
In summary, in the prior art arrangement, improvement of dimensional precision has been required, and there has been a possibility of the valve changing to an undesired operating condition.
Accordingly, it is one of the objectives of the present invention to solve these technical problems and provide ball valves for medium to low pressure service with improved productivity, and which are reduced in weight by use of smaller amounts of materials, high in rigidity, and excellent in wear resistance.
In another prior art arrangement in which valve parts are welded, rust often occurs due to degeneration of material due to local high temperatures caused by welding.
It is another objective of the present invention to provide ball valves for medium to low pressure service, without requiring welding, and which hence are free of rust attributable to welding, so as to be used safely for long periods of time.